Phytoplankton use sunlight to gain energy through photosynthesis. As a result of the Law of Conservation of Energy, phytoplankton cannot gain more energy than it consumes. A closed system consisting o

Phytoplankton use sunlight to gain energy through photosynthesis. As a result of the Law of Conservation of Energy, phytoplankton cannot gain more energy than it consumes. A closed system consisting of an aquarium, phytoplankton, and sunlight is set up. Which of the following methods would best demonstrate the Law of Conservation of Energy?